gcc/ada/sem_attr.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             S E M _ A T T R                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2014, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- You should have received a copy of the GNU General Public License along  --
  19 -- with this program; see file COPYING3.  If not see                        --
  20 -- <http://www.gnu.org/licenses/>.                                          --
  21 --                                                                          --
  22 -- GNAT was originally developed  by the GNAT team at  New York University. --
  23 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  24 --                                                                          --
  25 ------------------------------------------------------------------------------
  26
  27 --  Attribute handling is isolated in a separate package to ease the addition
  28 --  of implementation defined attributes. Logically this processing belongs
  29 --  in chapter 4. See Sem_Ch4 for a description of the relation of the
  30 --  Analyze and Resolve routines for expression components.
  31
  32 --  This spec also documents all GNAT implementation defined pragmas
  33
  34 with Exp_Tss; use Exp_Tss;
  35 with Namet;   use Namet;
  36 with Snames;  use Snames;
  37 with Types;   use Types;
  38
  39 package Sem_Attr is
  40
  41    -----------------------------------------
  42    -- Implementation Dependent Attributes --
  43    -----------------------------------------
  44
  45    --  This section describes the implementation dependent attributes
  46    --  provided in GNAT, as well as constructing an array of flags
  47    --  indicating which attributes these are.
  48
  49    Attribute_Impl_Def : Attribute_Class_Array := Attribute_Class_Array'(
  50
  51       ------------------
  52       -- Abort_Signal --
  53       ------------------
  54
  55       Attribute_Abort_Signal => True,
  56       --  Standard'Abort_Signal (Standard is the only allowed prefix) provides
  57       --  the entity for the special exception used to signal task abort or
  58       --  asynchronous transfer of control. Normally this attribute should only
  59       --  be used in the tasking runtime (it is highly peculiar, and completely
  60       --  outside the normal semantics of Ada, for a user program to intercept
  61       --  the abort exception).
  62
  63       ------------------
  64       -- Address_Size --
  65       ------------------
  66
  67       Attribute_Address_Size => True,
  68       --  Standard'Address_Size (Standard is the only allowed prefix) is
  69       --  a static constant giving the number of bits in an Address. It
  70       --  is used primarily for constructing the definition of Memory_Size
  71       --  in package Standard, but may be freely used in user programs.
  72       --  This is a static attribute.
  73
  74       ---------------
  75       -- Asm_Input --
  76       ---------------
  77
  78       Attribute_Asm_Input => True,
  79       --  Used only in conjunction with the Asm subprograms in package
  80       --  Machine_Code to construct machine instructions. See documentation
  81       --  in package Machine_Code in file s-maccod.ads.
  82
  83       ----------------
  84       -- Asm_Output --
  85       ----------------
  86
  87       Attribute_Asm_Output => True,
  88       --  Used only in conjunction with the Asm subprograms in package
  89       --  Machine_Code to construct machine instructions. See documentation
  90       --  in package Machine_Code in file s-maccod.ads.
  91
  92       ---------
  93       -- Bit --
  94       ---------
  95
  96       Attribute_Bit => True,
  97       --  Obj'Bit, where Obj is any object, yields the bit offset within the
  98       --  storage unit (byte) that contains the first bit of storage allocated
  99       --  for the object. The attribute value is of type Universal_Integer,
 100       --  and is always a non-negative number not exceeding the value of
 101       --  System.Storage_Unit.
 102       --
 103       --  For an object that is a variable or a constant allocated in a
 104       --  register, the value is zero. (The use of this attribute does not
 105       --  force the allocation of a variable to memory).
 106       --
 107       --  For an object that is a formal parameter, this attribute applies to
 108       --  either the matching actual parameter or to a copy of the matching
 109       --  actual parameter.
 110       --
 111       --  For an access object the value is zero. Note that Obj.all'Bit is
 112       --  subject to an Access_Check for the designated object. Similarly
 113       --  for a record component X.C'Bit is subject to a discriminant check
 114       --  and X(I).Bit and X(I1..I2)'Bit are subject to index checks.
 115       --
 116       --  This attribute is designed to be compatible with the DEC Ada
 117       --  definition and implementation of the Bit attribute.
 118
 119       ------------------
 120       -- Code_Address --
 121       ------------------
 122
 123       Attribute_Code_Address => True,
 124       --  The reference subp'Code_Address, where subp is a subprogram entity,
 125       --  gives the address of the first generated instruction for the sub-
 126       --  program. This is often, but not always the same as the 'Address
 127       --  value, which is the address to be used in a call. The differences
 128       --  occur in the case of a nested procedure (where Address yields the
 129       --  address of the trampoline code used to load the static link), and on
 130       --  some systems which use procedure descriptors (in which case Address
 131       --  yields the address of the descriptor).
 132
 133       -----------------------
 134       -- Default_Bit_Order --
 135       -----------------------
 136
 137       Attribute_Default_Bit_Order => True,
 138       --  Standard'Default_Bit_Order (Standard is the only permissible prefix)
 139       --  provides the value System.Default_Bit_Order as a Pos value (0 for
 140       --  High_Order_First, 1 for Low_Order_First). This is used to construct
 141       --  the definition of Default_Bit_Order in package System. This is a
 142       --  static attribute.
 143
 144       ----------------------------------
 145       -- Default_Scalar_Storage_Order --
 146       ----------------------------------
 147
 148       Attribute_Default_Scalar_Storage_Order => True,
 149       --  Standard'Default_Scalar_Storage_Order (Standard is the
 150       --  only permissible prefix) provides the current value of the
 151       --  default scalar storage order (as specified using pragma
 152       --  Default_Scalar_Storage_Order, or equal to Default_Bit_Order if
 153       --  unspecified) as a System.Bit_Order value. This is a static attribute.
 154
 155       ---------------
 156       -- Elab_Body --
 157       ---------------
 158
 159       Attribute_Elab_Body => True,
 160       --  This attribute can only be applied to a program unit name. It
 161       --  returns the entity for the corresponding elaboration procedure for
 162       --  elaborating the body of the referenced unit. This is used in the main
 163       --  generated elaboration procedure by the binder, and is not normally
 164       --  used in any other context, but there may be specialized situations in
 165       --  which it is useful to be able to call this elaboration procedure from
 166       --  Ada code, e.g. if it is necessary to do selective reelaboration to
 167       --  fix some error.
 168
 169       --------------------
 170       -- Elab_Subp_Body --
 171       --------------------
 172
 173       Attribute_Elab_Subp_Body => True,
 174       --  This attribute can only be applied to a library level subprogram
 175       --  name and is only relevant in CodePeer mode. It returns the entity
 176       --  for the corresponding elaboration procedure for elaborating the body
 177       --  of the referenced subprogram unit. This is used in the main generated
 178       --  elaboration procedure by the binder in CodePeer mode only.
 179
 180       ---------------
 181       -- Elab_Spec --
 182       ---------------
 183
 184       Attribute_Elab_Spec => True,
 185       --  This attribute can only be applied to a program unit name. It
 186       --  returns the entity for the corresponding elaboration procedure for
 187       --  elaborating the spec of the referenced unit. This is used in the main
 188       --  generated elaboration procedure by the binder, and is not normally
 189       --  used in any other context, but there may be specialized situations in
 190       --  which it is useful to be able to call this elaboration procedure from
 191       --  Ada code, e.g. if it is necessary to do selective reelaboration to
 192       --  fix some error.
 193
 194       ----------------
 195       -- Elaborated --
 196       ----------------
 197
 198       Attribute_Elaborated => True,
 199       --  Lunit'Elaborated, where Lunit is a library unit, yields a boolean
 200       --  value indicating whether or not the body of the designated library
 201       --  unit has been elaborated yet.
 202
 203       --------------
 204       -- Enum_Rep --
 205       --------------
 206
 207       Attribute_Enum_Rep => True,
 208       --  For every enumeration subtype S, S'Enum_Rep denotes a function
 209       --  with the following specification:
 210       --
 211       --    function S'Enum_Rep (Arg : S'Base) return universal_integer;
 212       --
 213       --  The function returns the representation value for the given
 214       --  enumeration value. This will be equal to the 'Pos value in the
 215       --  absence of an enumeration representation clause. This is a static
 216       --  attribute (i.e. the result is static if the argument is static).
 217
 218       --------------
 219       -- Enum_Val --
 220       --------------
 221
 222       Attribute_Enum_Val => True,
 223       --  For every enumeration subtype S, S'Enum_Val denotes a function with
 224       --  the following specification:
 225       --
 226       --    function S'Enum_Val (Arg : universal_integer) return S'Base;
 227       --
 228       --  This function performs the inverse transformation to Enum_Rep. Given
 229       --  a representation value for the type, it returns the corresponding
 230       --  enumeration value. Constraint_Error is raised if no value of the
 231       --  enumeration type corresponds to the given integer value.
 232
 233       -----------------
 234       -- Fixed_Value --
 235       -----------------
 236
 237       Attribute_Fixed_Value => True,
 238       --  For every fixed-point type S, S'Fixed_Value denotes a function
 239       --  with the following specification:
 240       --
 241       --    function S'Fixed_Value (Arg : universal_integer) return S;
 242       --
 243       --  The value returned is the fixed-point value V such that
 244       --
 245       --    V = Arg * S'Small
 246       --
 247       --  The effect is thus equivalent to first converting the argument to
 248       --  the integer type used to represent S, and then doing an unchecked
 249       --  conversion to the fixed-point type. This attribute is primarily
 250       --  intended for use in implementation of the input-output functions
 251       --  for fixed-point values.
 252
 253       -----------------------
 254       -- Has_Discriminants --
 255       -----------------------
 256
 257       Attribute_Has_Discriminants => True,
 258       --  Gtyp'Has_Discriminants, where Gtyp is a generic formal type, yields
 259       --  a Boolean value indicating whether or not the actual instantiation
 260       --  type has discriminants.
 261
 262       ---------
 263       -- Img --
 264       ---------
 265
 266       Attribute_Img => True,
 267       --  The 'Img function is defined for any prefix, P, that denotes an
 268       --  object of scalar type T. P'Img is equivalent to T'Image (P). This
 269       --  is convenient for debugging. For example:
 270       --
 271       --     Put_Line ("X = " & X'Img);
 272       --
 273       --  has the same meaning as the more verbose:
 274       --
 275       --     Put_Line ("X = " & Temperature_Type'Image (X));
 276       --
 277       --  where Temperature_Type is the subtype of the object X.
 278
 279       -------------------
 280       -- Integer_Value --
 281       -------------------
 282
 283       Attribute_Integer_Value => True,
 284       --  For every integer type S, S'Integer_Value denotes a function
 285       --  with the following specification:
 286       --
 287       --    function S'Integer_Value (Arg : universal_fixed) return S;
 288       --
 289       --  The value returned is the integer value V, such that
 290       --
 291       --    Arg = V * fixed-type'Small
 292       --
 293       --  The effect is thus equivalent to first doing an unchecked convert
 294       --  from the fixed-point type to its corresponding implementation type,
 295       --  and then converting the result to the target integer type. This
 296       --  attribute is primarily intended for use in implementation of the
 297       --  standard input-output functions for fixed-point values.
 298
 299       Attribute_Invalid_Value => True,
 300       --  For every scalar type, S'Invalid_Value designates an undefined value
 301       --  of the type. If possible this value is an invalid value, and in fact
 302       --  is identical to the value that would be set if Initialize_Scalars
 303       --  mode were in effect (including the behavior of its value on
 304       --  environment variables or binder switches). The intended use is to
 305       --  set a value where initialization is required (e.g. as a result of the
 306       --  coding standards in use), but logically no initialization is needed,
 307       --  and the value should never be accessed.
 308
 309       Attribute_Loop_Entry => True,
 310       --  For every object of a non-limited type, S'Loop_Entry [(Loop_Name)]
 311       --  denotes the constant value of prefix S at the point of entry into the
 312       --  related loop. The type of the attribute is the type of the prefix.
 313
 314       ------------------
 315       -- Machine_Size --
 316       ------------------
 317
 318       Attribute_Machine_Size => True,
 319       --  This attribute is identical to the Object_Size attribute. It is
 320       --  provided for compatibility with the DEC attribute of this name.
 321
 322       -----------------------
 323       -- Maximum_Alignment --
 324       -----------------------
 325
 326       Attribute_Maximum_Alignment => True,
 327       --  Standard'Maximum_Alignment (Standard is the only permissible prefix)
 328       --  provides the maximum useful alignment value for the target. This is a
 329       --  static value that can be used to specify the alignment for an object,
 330       --  guaranteeing that it is properly aligned in all cases. The time this
 331       --  is useful is when an external object is imported and its alignment
 332       --  requirements are unknown. This is a static attribute.
 333
 334       --------------------
 335       -- Mechanism_Code --
 336       --------------------
 337
 338       Attribute_Mechanism_Code => True,
 339       --  function'Mechanism_Code yields an integer code for the mechanism
 340       --  used for the result of function, and subprogram'Mechanism_Code (n)
 341       --  yields the mechanism used for formal parameter number n (a static
 342       --  integer value, 1 = first parameter). The code returned is:
 343       --
 344       --     1 = by copy (value)
 345       --     2 = by reference
 346       --     3 = by descriptor (default descriptor type)
 347       --     4 = by descriptor (UBS  unaligned bit string)
 348       --     5 = by descriptor (UBSB aligned bit string with arbitrary bounds)
 349       --     6 = by descriptor (UBA  unaligned bit array)
 350       --     7 = by descriptor (S    string, also scalar access type parameter)
 351       --     8 = by descriptor (SB   string with arbitrary bounds)
 352       --     9 = by descriptor (A    contiguous array)
 353       --    10 = by descriptor (NCA  non-contiguous array)
 354
 355       --------------------
 356       -- Null_Parameter --
 357       --------------------
 358
 359       Attribute_Null_Parameter => True,
 360       --  A reference T'Null_Parameter denotes an (imaginary) object of type
 361       --  or subtype T allocated at (machine) address zero. The attribute is
 362       --  allowed only as the default expression of a formal parameter, or
 363       --  as an actual expression of a subprogram call. In either case, the
 364       --  subprogram must be imported.
 365       --
 366       --  The identity of the object is represented by the address zero in
 367       --  the argument list, independent of the passing mechanism (explicit
 368       --  or default).
 369       --
 370       --  The reason that this capability is needed is that for a record or
 371       --  other composite object passed by reference, there is no other way
 372       --  of specifying that a zero address should be passed.
 373
 374       -----------------
 375       -- Object_Size --
 376       -----------------
 377
 378       Attribute_Object_Size => True,
 379       --  Type'Object_Size is the same as Type'Size for all types except
 380       --  fixed-point types and discrete types. For fixed-point types and
 381       --  discrete types, this attribute gives the size used for default
 382       --  allocation of objects and components of the size. See section in
 383       --  Einfo ("Handling of type'Size values") for further details.
 384
 385       -------------------------
 386       -- Passed_By_Reference --
 387       -------------------------
 388
 389       Attribute_Passed_By_Reference => True,
 390       --  T'Passed_By_Reference for any subtype T returns a boolean value that
 391       --  is true if the type is normally passed by reference and false if the
 392       --  type is normally passed by copy in calls. For scalar types, the
 393       --  result is always False and is static. For non-scalar types, the
 394       --  result is non-static (since it is computed by Gigi).
 395
 396       ------------------
 397       -- Range_Length --
 398       ------------------
 399
 400       Attribute_Range_Length => True,
 401       --  T'Range_Length for any discrete type T yields the number of values
 402       --  represented by the subtype (zero for a null range). The result is
 403       --  static for static subtypes. Note that Range_Length applied to the
 404       --  index subtype of a one dimensional array always gives the same result
 405       --  as Range applied to the array itself. The result is of type universal
 406       --  integer.
 407
 408       ---------
 409       -- Ref --
 410       ---------
 411
 412       Attribute_Ref => True,
 413       --  System.Address'Ref (Address is the only permissible prefix) is
 414       --  equivalent to System'To_Address, provided for compatibility with
 415       --  other compilers.
 416
 417       ------------------
 418       -- Storage_Unit --
 419       ------------------
 420
 421       Attribute_Storage_Unit => True,
 422       --  Standard'Storage_Unit (Standard is the only permissible prefix)
 423       --  provides the value System.Storage_Unit, and is intended primarily
 424       --  for constructing this definition in package System (see note above
 425       --  in Default_Bit_Order description). The is a static attribute.
 426
 427       ---------------
 428       -- Stub_Type --
 429       ---------------
 430
 431       Attribute_Stub_Type => True,
 432       --  The GNAT implementation of remote access-to-classwide types is
 433       --  organised as described in AARM E.4(20.t): a value of an RACW type
 434       --  (designating a remote object) is represented as a normal access
 435       --  value, pointing to a "stub" object which in turn contains the
 436       --  necessary information to contact the designated remote object. A
 437       --  call on any dispatching operation of such a stub object does the
 438       --  remote call, if necessary, using the information in the stub object
 439       --  to locate the target partition, etc.
 440       --
 441       --  For a prefix T that denotes a remote access-to-classwide type,
 442       --  T'Stub_Type denotes the type of the corresponding stub objects.
 443       --
 444       --  By construction, the layout of T'Stub_Type is identical to that of
 445       --  System.Partition_Interface.RACW_Stub_Type (see implementation notes
 446       --  in body of Exp_Dist).
 447
 448       -----------------
 449       -- Target_Name --
 450       -----------------
 451
 452       Attribute_Target_Name => True,
 453       --  Standard'Target_Name yields the string identifying the target for the
 454       --  compilation, taken from Sdefault.Target_Name.
 455
 456       ----------------
 457       -- To_Address --
 458       ----------------
 459
 460       Attribute_To_Address => True,
 461       --  System'To_Address (System is the only permissible prefix) is a
 462       --  function that takes any integer value, and converts it into an
 463       --  address value. The semantics is to first convert the integer value to
 464       --  type Integer_Address according to normal conversion rules, and then
 465       --  to convert this to an address using the same semantics as the
 466       --  System.Storage_Elements.To_Address function. The important difference
 467       --  is that this is a static attribute so it can be used in
 468       --  initializations in preelaborate packages.
 469
 470       ----------------
 471       -- Type_Class --
 472       ----------------
 473
 474       Attribute_Type_Class => True,
 475       --  T'Type_Class for any type or subtype T yields the value of the type
 476       --  class for the full type of T. If T is a generic formal type, then the
 477       --  value is the value for the corresponding actual subtype. The value of
 478       --  this attribute is of type System.Aux_DEC.Type_Class, which has the
 479       --  following definition:
 480       --
 481       --    type Type_Class is
 482       --      (Type_Class_Enumeration,
 483       --       Type_Class_Integer,
 484       --       Type_Class_Fixed_Point,
 485       --       Type_Class_Floating_Point,
 486       --       Type_Class_Array,
 487       --       Type_Class_Record,
 488       --       Type_Class_Access,
 489       --       Type_Class_Task,
 490       --       Type_Class_Address);
 491       --
 492       --  Protected types yield the value Type_Class_Task, which thus applies
 493       --  to all concurrent types. This attribute is designed to be compatible
 494       --  with the DEC Ada attribute of the same name.
 495       --
 496       --  Note: if pragma Extend_System is used to merge the definitions of
 497       --  Aux_DEC into System, then the type Type_Class can be referenced
 498       --  as an entity within System, as can its enumeration literals.
 499
 500       -----------------
 501       -- UET_Address --
 502       -----------------
 503
 504       Attribute_UET_Address => True,
 505       --  Unit'UET_Address, where Unit is a program unit, yields the address
 506       --  of the unit exception table for the specified unit. This is only
 507       --  used in the internal implementation of exception handling. See the
 508       --  implementation of unit Ada.Exceptions for details on its use.
 509
 510       ------------------------------
 511       -- Universal_Literal_String --
 512       ------------------------------
 513
 514       Attribute_Universal_Literal_String => True,
 515       --  The prefix of 'Universal_Literal_String must be a named number.
 516       --  The static result is the string consisting of the characters of
 517       --  the number as defined in the original source. This allows the
 518       --  user program to access the actual text of named numbers without
 519       --  intermediate conversions and without the need to enclose the
 520       --  strings in quotes (which would preclude their use as numbers).
 521
 522       -------------------------
 523       -- Unrestricted_Access --
 524       -------------------------
 525
 526       Attribute_Unrestricted_Access => True,
 527       --  The Unrestricted_Access attribute is similar to Access except that
 528       --  all accessibility and aliased view checks are omitted. This is very
 529       --  much a user-beware attribute. Basically its status is very similar
 530       --  to Address, for which it is a desirable replacement where the value
 531       --  desired is an access type. In other words, its effect is identical
 532       --  to first taking 'Address and then doing an unchecked conversion to
 533       --  a desired access type. Note that in GNAT, but not necessarily in
 534       --  other implementations, the use of static chains for inner level
 535       --  subprograms means that Unrestricted_Access applied to a subprogram
 536       --  yields a value that can be called as long as the subprogram is in
 537       --  scope (normal Ada 95 accessibility rules restrict this usage).
 538
 539       ---------------
 540       -- VADS_Size --
 541       ---------------
 542
 543       Attribute_VADS_Size => True,
 544       --  Typ'VADS_Size yields the Size value typically yielded by some Ada 83
 545       --  compilers. The differences between VADS_Size and Size is that for
 546       --  scalar types for which no Size has been specified, VADS_Size yields
 547       --  the Object_Size rather than the Value_Size. For example, while
 548       --  Natural'Size is typically 31, the value of Natural'VADS_Size is 32.
 549       --  For all other types, Size and VADS_Size yield the same value.
 550
 551       -------------------
 552       -- Valid_Scalars --
 553       -------------------
 554
 555       Attribute_Valid_Scalars => True,
 556       --  Obj'Valid_Scalars can be applied to any object. The result depends
 557       --  on the type of the object:
 558       --
 559       --    For a scalar type, the result is the same as obj'Valid
 560       --
 561       --    For an array object, the result is True if the result of applying
 562       --    Valid_Scalars to every component is True. For an empty array the
 563       --    result is True.
 564       --
 565       --    For a record object, the result is True if the result of applying
 566       --    Valid_Scalars to every component is True. For class-wide types,
 567       --    only the components of the base type are checked. For variant
 568       --    records, only the components actually present are checked. The
 569       --    discriminants, if any, are also checked. If there are no components
 570       --    or discriminants, the result is True.
 571       --
 572       --    For any other type that has discriminants, the result is True if
 573       --    the result of applying Valid_Scalars to each discriminant is True.
 574       --
 575       --    For all other types, the result is always True
 576       --
 577       --  A warning is given for a trivially True result, when the attribute
 578       --  is applied to an object that is not of scalar, array, or record
 579       --  type, or in the composite case if no scalar subcomponents exist. For
 580       --  a variant record, the warning is given only if none of the variants
 581       --  have scalar subcomponents. In addition, the warning is suppressed
 582       --  for private types, or generic formal types in an instance.
 583
 584       ----------------
 585       -- Value_Size --
 586       ----------------
 587
 588       Attribute_Value_Size => True,
 589       --  Type'Value_Size is the number of bits required to represent value of
 590       --  the given subtype. It is the same as Type'Size, but, unlike Size, may
 591       --  be set for non-first subtypes. See section in Einfo ("Handling of
 592       --  type'Size values") for further details.
 593
 594       ---------------
 595       -- Word_Size --
 596       ---------------
 597
 598       Attribute_Word_Size => True,
 599       --  Standard'Word_Size (Standard is the only permissible prefix)
 600       --  provides the value System.Word_Size, and is intended primarily
 601       --  for constructing this definition in package System (see note above
 602       --  in Default_Bit_Order description). This is a static attribute.
 603
 604       others => False);
 605
 606    -----------------
 607    -- Subprograms --
 608    -----------------
 609
 610    procedure Analyze_Attribute (N : Node_Id);
 611    --  Performs bottom up semantic analysis of an attribute. Note that the
 612    --  parser has already checked that type returning attributes appear only
 613    --  in appropriate contexts (i.e. in subtype marks, or as prefixes for
 614    --  other attributes).
 615
 616    function Name_Implies_Lvalue_Prefix (Nam : Name_Id) return Boolean;
 617    --  Determine whether the name of an attribute reference categorizes its
 618    --  prefix as an lvalue. The following attributes fall under this bracket
 619    --  by directly or indirectly modifying their prefixes.
 620    --     Access
 621    --     Address
 622    --     Input
 623    --     Read
 624    --     Unchecked_Access
 625    --     Unrestricted_Access
 626
 627    procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id);
 628    --  Performs type resolution of attribute. If the attribute yields a
 629    --  universal value, mark its type as that of the context. On the other
 630    --  hand, if the context itself is universal (as in T'Val (T'Pos (X)), mark
 631    --  the type as being the largest type of that class that can be used at
 632    --  run-time. This is correct since either the value gets folded (in which
 633    --  case it doesn't matter what type of the class we give if, since the
 634    --  folding uses universal arithmetic anyway) or it doesn't get folded (in
 635    --  which case it is going to be dealt with at runtime, and the largest type
 636    --  is right).
 637
 638    function Stream_Attribute_Available
 639      (Typ          : Entity_Id;
 640       Nam          : TSS_Name_Type;
 641       Partial_View : Entity_Id := Empty) return Boolean;
 642    --  For a limited type Typ, return True if and only if the given attribute
 643    --  is available. For Ada 2005, availability is defined by 13.13.2(36/1).
 644    --  For Ada 95, an attribute is considered to be available if it has been
 645    --  specified using an attribute definition clause for the type, or for its
 646    --  full view, or for an ancestor of either. Parameter Partial_View is used
 647    --  only internally, when checking for an attribute definition clause that
 648    --  is not visible (Ada 95 only).
 649
 650 end Sem_Attr;